Re: [Help-gsl] Determinant of a matrix:

[Doug McKee]

I'm probably a little late (just joined the list today), but I ran into 
this exact problem about a week ago.  I never figured out why my call 
to gsl_linalg_LU_det didn't work, but I did come up with a work-around. 
 If I copy the function definition from the gsl source and rename the 
function my_gsl_linalg_LU_det in my own file, it works great.  All it 
does is multiply the elements of the diagonal.  I'd still love to know 
why the library call fails though.  Just makes me nervous that other 
functions are failing and I'm not noticing.

HTH,
Doug

> Thanks a lot for the reply.
>
> I am sorry, I did copy the matrix A into tmp_ptr. So, the code is like:
> (exactly as you suggested in the reply):
>
> double get_det(gsl_matrix * A) {
>   int sign=0; double det=0.0; int row_sq = A->size1;
>   gsl_permutation * p = gsl_permutation_calloc(row_sq);
>   gsl_matrix * tmp_ptr = gsl_matrix_calloc(row_sq, row_sq);
>   int * signum = &sign;
>   gsl_matrix_memcpy(tmp_ptr, A);
>   gsl_linalg_LU_decomp(tmp_ptr, p, signum);
>   det = gsl_linalg_LU_det(tmp_ptr, *signum);
>   gsl_permutation_free(p);
>   gsl_matrix_free(tmp_ptr);
>   return det;
> }
>
> It doesnt work, even for simple 2X2 or 3X3 matrices.
>
> > -Nomesh